4. Determine how many miRNAs start with each possible 5' nucleotide (A, C, G, T) - what is the most common 5' nt?

5. Determine how many miRNAs are 20, 21, 22, 23, and 24 nt. What is the most common length of miRNAs?

6. Extract all potential let-7 miRNA family members using grep, preserving the fasta format. miRNA families are determined by their seed sequence, positions 2-8 of the mature miRNA. The seed sequence of let-7 is: GAGGTAG.